Japanese Patent Laid-Open No. 2003-285787 and Japanese Patent Laid-Open No. 2003-261081 disclose technologies for inflating an air bag, which is activated by detecting an impact, in front of a rider in order to restrain the movement of the rider toward a front of a vehicle body due to impact while operating a two wheel vehicle.
Japanese Patent Laid-Open No. 2003-285787 discloses a technology wherein an air bag unit is disposed between a front end portion of a fuel tank and a meter panel. The unit is supported by a main frame of a large two wheel vehicle with a structure in which the fuel tank and a rider's seat are arranged in line and the fuel tank is held by a knee grip. Japanese Patent Laid-Open No. 2003-261081 discloses a technology wherein an air bag unit is installed below a front of a rider's seat in a two wheel vehicle having a structure in which a fuel tank and the rider's seat are similarly arranged in line and the fuel tank is held by a knee grip.
The technology of Japanese Patent Laid-Open No. 2003-285787 is intended for a two wheel vehicle having a structure in which a fuel tank is held by a knee grip. As described above, the two wheel vehicle has a main frame which extends towards a rear of a vehicle body from an upper end portion of a handle pipe and supports the fuel tank and the rider's seat. Thus, it is possible to dispose the air bag unit between the front end portion of the fuel tank and the meter panel, and to support the unit by the main frame. However, in a two wheel vehicle having a scooter structure, a main frame is bent downwardly in a U-shape in order to secure a wide footrest space. Thus, it is difficult to support an air bag unit by the main frame.
In the technology of Japanese Patent Laid-Open No. 2003-261081, since the air bag unit is disposed below the front of the rider seat, the rider seat is configured so as to have its front lifted up when the air bag is inflated. However, in the two wheel vehicle having the scooter structure, a rider is seated with his/her knees closed, thus making it difficult to have a structure in which the front of the rider seat is lifted up.